Exhaust emission control device with additive injector

ABSTRACT

An exhaust emission control apparatus is provided which is equipped with an additive injector to inject additive such as a urea aqueous solution into an exhaust pipe through which exhaust emissions flow. The exhaust pipe includes a straight section and a bent section. A catalyst such as a SCR (Selective Catalytic Reduction) catalyst is disposed downstream of the straight section. A hollow protrusion is formed on an outer peripheral wall of the bent section substantially in parallel to a longitudinal center line of the straight section. The protrusion has an opening formed in one of opposed ends thereof which communicates with inside the bent section. The additive injector is designed to produce a cone-shaped spray of additive and installed on the other end of the protrusion to inject the cone-shaped spray of additive into the exhaust pipe without interfering with at least a downstream edge of the opening.

CROSS REFERENCE TO RELATED DOCUMENT

The present application claims the benefit of Japanese PatentApplication No. 2006-342319 filed on Dec. 20, 2006, the disclosure ofwhich is totally incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to an exhaust emission controldevice equipped with an additive injector which may be used with an SCR(Selective Catalytic Reduction) system working to induce an exhaust gaspurification reaction using additive such as a urea aqueous solution.

2. Background Art

Urea SCR systems designed as exhaust emission control devices for use inelectric power plants, factories, or automobiles especially equippedwith diesel engines are now being developed and partially put inpractical use.

FIG. 5 illustrates a typical one of the urea SCR systems.

The urea SCR system includes generally an SCR catalyst 51, an exhaustpipe 52 extending between an exhaust emission source (i.e., anautomotive diesel engine) and the catalyst 51, and a urea solutioninjection valve 53. The catalyst 51 works to induce NOx reduction topurify exhaust gas flowing thereinto through the exhaust pipe 52. Theurea solution injection valve 53 is installed in the exhaust pipe 52 toinject or spray an aqueous urea (i.e., a urea aqueous solution) to aflow of the exhaust gas within the exhaust pipe 52 as a reducing agent.Specifically, the urea solution injection valve 53 is, as clearlyillustrated in FIG. 5, inclined to the length of the exhaust pipe 52 ata given angle to have a spray hole 53 a facing the catalyst 51 so as toorient the spray of the aqueous urea toward the catalyst 51.

In operation, the urea solution injection valve 53 sprays the aqueoussolution into the exhaust pipe 52. The aqueous solution is then carriedby the flow of exhaust gas to the catalyst 51 located downstream of theurea solution injection valve 53, so that the exhaust gas is purifiedthrough NOx reduction taken place on the catalyst 51. In the reductionof NOx emissions, the urea aqueous solution is hydrolyzed by the thermalenergy of the exhaust gas to produce ammonia (NH₃) which is, in turn,added to the NOx emissions, as selectively adsorbed by the catalyst 51,so that the NOx emissions react with the ammonia on the surface of thecatalyst 51 and are converted into harmless products.

The exhaust pipe 52 is sometimes shaped to have a bend depending uponthe layout of component parts of the vehicle. There are known ureasolution injection valves disposed in such a bend of the exhaust pipe.For instance, Japanese Patent First Publication Nos. 2001-3737 and2003-293739 and Translated PCT Publication No. 2001-516635 teach such atype of urea solution injection valve.

It is preferable that urea SCR systems having the urea solutioninjection valve installed in the bend of the exhaust pipe are designedto orient a stream of urea aqueous solution in the same direction as theflow of exhaust gas in order to mix the urea aqueous solution with theexhaust gas passing through the bend homogeneously and supply it to thecatalyst. However, the urea solution injection valves, as disclosed inthe above second and third publications, are so disposed as to beexposed inside the bend, so that they are subjected to intense heat ofthe exhaust gas.

The urea solution injection valve, as disclosed in the above firstpublication, is mounted in a protrusion extending outside the bend ofthe exhaust pipe in a direction opposite to the catalyst in order tominimize the exposure of the urea solution injection valve to theintense heat of exhaust gas. This structure is, however, needed toselect the length of the protrusion from the outer surface of the bendor regulate the angle of a cone-shaped spread of urea aqueous solutionaccurately in order to avoid the adhesion of a spray of the urea aqueoussolution to an inner wall of the protrusion, which may result ininstability in mixing the urea aqueous solution with the exhaust gashomogeneously.

SUMMARY OF THE INVENTION

It is therefore a principal object of the invention to avoid thedisadvantages of the prior art.

It is another object of the invention to provide an exhaust emissioncontrol device equipped with an additive injector which is designed toprotect the additive injector from intense heat of exhaust gas andensure the stability in an exhaust gas purification reaction usingadditive injected into exhaust gas.

According to one aspect of the invention, there is provided an exhaustemission control apparatus which may be used as a urea SCR (SelectiveCatalytic Reduction) system for automotive internal combustion engineswhich works to convert harmful emissions into less harmless substances.The exhaust emission control apparatus comprises: (a) an exhaust pipethrough which exhaust emissions flow, the exhaust pipe including astraight section and a bent section extending from the straight sectionin an upstream direction of a flow of the exhaust emissions; (b) acatalyst disposed downstream of the straight section of the exhaust pipein connection therewith; (c) a hollow protrusion having a lengthextending outside the exhaust pipe from a peripheral wall of the bentsection substantially in parallel to a longitudinal center line of thestraight section, the protrusion having a first end and a second endopposed to the first end, the protrusion having an opening formed in thefirst end which communicates with inside the bent section of the exhaustpipe; and (d) an additive injector designed to produce a cone-shapedspray of additive, the additive injector being installed in the secondend of the protrusion and oriented to inject the cone-shaped spray ofadditive into the exhaust pipe through the opening of the protrusionwithout interfering with at least a downstream edge of the opening. Theadditive is carried by the flow of the exhaust emissions downstream tothe catalyst and used in a given exhaust emission purification reaction,as induced by the catalyst, to purify the exhaust emissions.

Specifically, the protrusion extends outside the exhaust pipe. Theadditive injector is retained by the protrusion without being exposeddirectly to the exhaust emissions flowing through the exhaust pipe,thereby minimizing the transmission of intense heat of the exhaustemissions to the additive injector. Additionally, the additive injectoris also so held by the protrusion as to avoid the interference of thecone-shaped spray of the additive with at least the downstream edge ofthe opening that is a portion of the opening located farthest away fromthe additive injector. Further, the protrusion is formed to extendsubstantially parallel to the longitudinal center line of the straightsection of the exhaust pipe. The additive injector is secured to thesecond end of the protrusion. In other words, the center axis of thecone-shaped spray, that is, a path along which the additive is sprayedfrom the additive injector is aligned with the longitudinal center lineof the straight section of the exhaust pipe, thereby minimizing theadhesion of the additive to an inner wall of the protrusion and mixingthe additive to the exhaust emissions homogeneously which are, then,carried to the catalyst.

In the preferred mode of the invention, the additive injector is sooriented by the protrusion as to avoid interference of the cone-shapedspray of additive with an entire edge of the opening of the protrusion.

The protrusion has a cylindrical inner wall, thereby facilitatingmachining of the protrusion and also minimizing the adhesion of thespray of additive thereto.

The additive injector has a head in which a spray hole is formed. Thedistance between the downstream edge of the opening of the protrusionand the head of the additive injector is so selected as a function of anangle of spread of the additive, as sprayed from the additive injector,as to avoid interference of the cone-shaped spray of the additive withthe downstream edge of the opening of the protrusion.

The additive injector is oriented in alignment of an axis thereof withthat of the straight section of the exhaust pipe, thereby resulting in auniform distribution of the spray of additive over the straight sectionof the exhaust pipe and carrying a homogeneous mixture of the additiveand the exhaust emissions to the catalyst.

The additive injector may also be oriented in alignment of an axis withthat of the catalyst.

The additive injector may be designed to change the angle of spread ofthe additive. The additive injector is oriented to avoid interference ofthe cone-shaped spray of additive with at least the downstream edge ofthe opening when the angle of spread of the additive is maximized.

The exhaust pipe may also include a second bent section through whichthe exhaust gas flows. The second bent section communicates with thebent section and the straight section at a branch joint. The opening ofthe protrusion leads inside the exhaust pipe through a wall of thebranch joint. The protrusion extends outside the exhaust pipesubstantially in parallel to the longitudinal center line of thestraight section.

The bent section is curved smoothly or flexed to a right angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinbelow and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to limit the invention to the specific embodiments but are for thepurpose of explanation and understanding only.

In the drawings:

FIG. 1 is a schematic view which shows an exhaust emission controlapparatus according to the invention;

FIG. 2 is a partially enlarged sectional view of FIG. 1;

FIG. 3 is a side view which shows a first modification of installationof a urea solution injection valve installed in the exhaust emissioncontrol apparatus of FIG. 1;

FIG. 4( a) is a side view which shows a second modification ofinstallation of a urea solution injection valve installed in the exhaustemission control apparatus of FIG. 1;

FIG. 4( b) is a side view which shows a third modification ofinstallation of a urea solution injection valve installed in the exhaustemission control apparatus of FIG. 1; and

FIG. 5 is a partially sectional view which shows installation of a ureasolution injection valve used in a conventional urea SCR systems

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, particularly to FIG. 1, there is shown a ureaSCR (Selectively Catalytic Reduction) system according to the inventionwhich is engineered, like the one in FIG. 5, as an exhaust emissioncontrol device to convert NOx emissions contained in exhaust gas from anautomotive diesel engine (not shown) into harmless products.

The urea SCR system includes a DOC (Diesel Oxidation Catalyst) 21, anexhaust pipe 10, and a SCR (Selectively Catalytic Reduction) catalyst20, and a urea solution injection valve 50. The exhaust gas, as emittedfrom the diesel engine, flows through the exhaust pipe 10 in a directionA.

The urea solution injection valve 50 is installed in a portion theexhaust pipe 10 between the DOC 21 and the SCR catalyst 20. The ureasolution injection valve 50 is controlled in operation by a controller(not shown) to inject or spray a urea aqueous solution as a reducingagent (also called reducer) to the exhaust gas flowing from the DOC 21to the SCR catalyst 20. The urea aqueous solution is then carried by thestream of exhaust gas to the SCR catalyst 20 and used in NOx reduction.

Specifically, the SCR catalyst 20 works to induce the NOx reduction,that is, induce, for example, reactions below.

4NO+4NH₃+O₂

4N₂6H₂O  (1)

6HO₂+8NH₂

7N₂+12H₂O  (2)

NO+NO₂+2NH₃

2N₂+2H₂O  (3)

The ammonia (NH₃) that is used as a reducing agent for the NOx reductionin the above reaction formulas is supplied by the urea solutioninjection valve 50 disposed upstream of the SCR catalyst 20.

The urea solution injection valve 50 is of a known structure similar totypical fuel injectors and works to produce, as indicated by an arrow Fin FIG. 2, a cone-shaped spray of urea aqueous solution through a sprayhole 75 formed in a head thereof. The urea solution injection valve 50is supplied with the urea aqueous solution from a urea solution tank(not shown) through a urea solution supply pipe.

The exhaust pipe 10 is, as can be seen from FIG. 1, made up of threesections: a hollow cylindrical straight section 11 joined directly tothe SCR catalyst 20, a curved section 12 extending from the straightsection 11, and a curved section 13 joined to the DOC 21. The curvedsection 13 is bent in a direction opposite to the curved section 12 andconnected thereto to define an S-shaped portion of the exhaust pipe 10.The curved section 12 has formed thereon a protrusion 14 in which theurea solution injection valve 50 is installed.

The protrusion 14 is hollow cylindrical and opens into the curvedsection 12 of the exhaust pipe 10, as illustrated in FIG. 1, inalignment of a longitudinal center line (i.e., an axis) 25 thereof witha longitudinal center line of the straight section 11. The protrusion 14extends from an outer peripheral wall of the curved section 12 away fromthe straight section 11. The protrusion 14 may be machined to have acylindrical inner wall. The SCR catalyst 20 is disposed in alignment ofa longitudinal center line thereof with the longitudinal center line ofthe straight section 11.

The protrusion 14 has an end wall 18 to which the urea solutioninjection valve 50 is secured. Specifically, the urea solution injectionvalve 50 is joined to the end wall 18 of the protrusion 14 through aheat insulator 22 to have the head (i.e., the spray hole 75) thereofexposed inside the protrusion 14. The spray hole 75 is, as can be seenin FIG. 2, formed in the center of a top end wall of the head of theurea solution injection valve 50 to align a jet of urea aqueous solutionwith the SCR catalyst 20.

The urea solution injection valve 50 is so retained by the end wall 18as to orient the cone-shaped spray F of urea aqueous solution to an ovalopening 65, as defined by a joint between the curved section 12 of theexhaust pipe 10 and the protrusion 14, without physically interferingwith a lower edge 15 of the oval opening 65 (i.e., the most downstreamportion of the joint between the curved section 12 and the protrusion 14in a direction of flow of the exhaust gas). In other words, the angle θof spread of the urea aqueous solution and the distance L between thelower edge 15 of the opening 65 and the top end (i.e., the spray hole75) of the urea solution injection valve 50 are so selected as to avoidthe adhesion of the urea aqueous solution to the lower edge 15 of theopening 65. In this embodiment, the angle θ and the distance L are alsoselected so as to avoid the interference of the cone-shaped spray F ofurea aqueous solution with an upper edge 16 of the oval opening 65(i.e., the most upstream portion of the joint between the curved section12 and the protrusion 14 in the direction of flow of the exhaust gas).It is also advisable that the angle θ and the distance L be selected soas to avoid the interference of the cone-shaped spray F of urea aqueoussolution with an entire edge of the oval opening 65. The urea solutioninjection valve 50 may be designed to change the angle θ of spread ofthe urea aqueous solution in response to a change in operating conditionof the engine. In this case, it is advisable that the urea solutioninjection valve 50 be installed in the protrusion 14 so that the sprayof urea aqueous solution does not interfere with at least the lower edge15 of the opening 65 when the angle θ is maximized.

The beneficial advantages of the urea SCR system will be describedbelow.

The urea solution injection valve 50 is, as described above, secured tothe end wall 18 of the protrusion 14, so that it is not exposed directlyto the intense heat of the exhaust gas flowing, as indicated by an arrowA, in the exhaust pipe 10. The use of the heat insulator 22 furtherminimizes the transmission of the heat to the urea solution injectionvalve 50.

The urea solution injection valve 50 is oriented in alignment of thelongitudinal center line thereof with that of the straight section 11 ofthe exhaust pipe 10 (i.e., the SCR catalyst 20), thereby directing thecone-shaped spray F of the urea aqueous solution uniformly over theentire inlet surface of the SCR catalyst 20. Specifically, the ureaaqueous solution and the exhaust gas which are mixed homogeneously reachthe entire surface of the SCR catalyst 20.

The location where the urea solution injection valve 50 is mounted onthe protrusion 14 and the structure of the protrusion 14 are sodetermined that the urea aqueous solution is injected into the curvedsection 12 of the exhaust pipe 10 without interfering with at least thelower edge 15 of the opening 65 of the exhaust pipe 10, thus mixing theurea aqueous solution with the exhaust gas within the exhaust pipe 10without the adhesion thereof to the inner wall of the protrusion 14.

FIG. 3 illustrates the first modification of the installation of theurea solution injection valve 50 to the exhaust pipe 10.

Specifically, the exhaust pipe 10 includes an L-shaped section 12 ainstead of the curved section 12 of FIG. 1. The L-shaped section 12 a isbent at right angles and connected between the sections 11 and 13. Theprotrusion 14 extends from the L-shaped section 12 a away from thestraight section 11. The urea solution injection valve 50 is installedin the protrusion 14 in alignment of the longitudinal center linethereof with that of the straight section 11.

FIG. 4( a) illustrates the second modification of the installation ofthe urea solution injection valve 50.

The exhaust pipe 10 includes two curved sections 12 b and 12 c each ofwhich is joined to one of DOCs (not shown). The curved sections 12 bcommunicate with the SCR catalyst 20 through the straight section 11.The protrusion 14 is formed on a branch joint 19 of the curved sections12 b and 12 c. The urea solution injection valve 50 is disposed in theprotrusion 14 in alignment of the longitudinal center line thereof withthat of the straight section 11 (i.e., the SCR catalyst 20).

FIG. 4( b) illustrates the third modification of the installation of theurea solution injection valve 50.

The exhaust pipe 10 includes a T-shaped section 12 e joined at twoinlets thereof to DOCs (not shown), respectively. The T-shaped section12 e is also joined at an outlet thereof to the SCR catalyst 20 throughthe straight section 11. The protrusion 14 is formed on the outersurface of the T-shaped section 12 e in alignment with the outlet of theT-shaped section 12 e. The urea solution injection valve 50 is disposedin the protrusion 14 in alignment of the longitudinal center linethereof with that of the straight section 11 (i.e., the SCR catalyst20).

The urea SCR system may be used with engines other than diesel enginessuch as gasoline engines (e.g., spark ignition engines) or another typeof exhaust emission control device. The urea SCR system may also bedesigned to use a reducing agent other than urea.

While the present invention has been disclosed in terms of the preferredembodiments in order to facilitate better understanding thereof itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodifications to the shown embodiments witch can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. An exhaust emission control apparatus comprising: an exhaust pipethrough which exhaust emission flow, said exhaust pipe including astraight section and a bent section extending from the straight sectionin an upstream direction of a flow of the exhaust emissions; a catalystdisposed downstream of the straight section of said exhaust pipe inconnection therewith; a hollow protrusion having a length extendingoutside the said exhaust pipe from a peripheral wall of the bent sectionsubstantially in parallel to a longitudinal center line of the straightsection, said protrusion having a first end and a second end opposed tothe first end, said protrusion having an opening formed in the first endwhich communicates with inside the bent section of said exhaust pipe;and an additive injector designed to produce a cone-shaped spray ofadditive, said additive injector being installed in the second end ofsaid protrusion and oriented to inject the cone-shaped spray of additiveinto said exhaust pipe through the opening of said protrusion withoutinterfering with at least a downstream edge of the opening, the additivebeing carried by the flow of the exhaust emissions downstream to saidcatalyst and used in a given exhaust emission purification reaction, asinduced by said catalyst, to purify the exhaust emissions.
 2. An exhaustemission control apparatus as set forth in claim 1, wherein saidadditive injector is so oriented by said protrusion as to avoidinterference of the cone-shaped spray of additive with an entire edge ofthe opening of said protrusion.
 3. An exhaust emission control apparatusas set forth in claim 1, wherein said protrusion has a cylindrical innerwall.
 4. An exhaust emission control apparatus as set forth in claim 1,wherein said additive injector has a head in which a spray hole isformed, and wherein a distance between the downstream edge of theopening of said protrusion and the head of said additive injector is soselected as a function of an angle of spread of the additive, as sprayedfrom said additive injector, as to avoid interference of the cone-shapedspray of the additive with the downstream edge of the opening of saidprotrusion.
 5. An exhaust emission control apparatus as set forth inclaim 1, wherein said additive injector is oriented in alignment of anaxis thereof with that of the straight section of said exhaust pipe. 6.An exhaust emission control apparatus as set forth in claim 1, whereinsaid additive injector is oriented in alignment of an axis with that ofsaid catalyst.
 7. An exhaust emission control apparatus as set forth inclaim 4, wherein said additive injector is designed to change the angleof spread of the additive, and wherein said additive injector isoriented to avoid interference of the cone-shaped spray of additive withat least the downstream edge of the opening when the angle of spread ofthe additive is maximized.
 8. An exhaust emission control apparatus asset forth in claim 1, wherein said exhaust pipe also includes a secondbent section through which the exhaust gas flows, said second bentsection communicating with the bent section and the straight section ata branch joint, and wherein the opening of said protrusion leadinginside said exhaust pipe through a wall of the branch joint, saidprotrusion extending outside said exhaust pipe substantially in parallelto the longitudinal center line of the straight section.
 9. An exhaustemission control apparatus as set forth in claim 1, wherein the bentsection is curved.
 10. An exhaust emission control apparatus as setforth in claim 1, wherein the bent section is flexed to a right angle.